ABS wheel speed sensor (inductive) - voltage

The purpose of this test is to evaluate the operation of an Antilock Braking System (ABS) inductive wheel speed sensor based upon its output voltage and frequency.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

Access to individual wheel speed sensors may be difficult.

All wheel speed sensors connect to the ABS control module, which is usually located in the engine bay.

  1. Use manufacturer data to identify the wheel speed sensor circuits.
  2. Connect PicoScope to the suspect sensor(s).
  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Turn the ignition on but do not start the engine.
  5. Select Go or press the space bar to see live data.
  6. With the suspect wheel(s) raised, rotate by hand. This will be sufficient to produce an output from a good speed sensor.
  7. With your live waveform on screen select Stop or press the space bar to stop your capture.
  8. Use the Waveform Buffer and Zoom tools to examine your waveform.

NOTE:

PicoScope can be connected to gather waveforms from 2 or more wheel speed sensors whilst conducting a road test. In these conditions, the computer and screen must be out of the driver's view and/or operated by a second technician.

Waveform notes

These waveforms have the following characteristics:

The oscillation frequency and amplitude increase with increasing wheel speed.

One wheel

Channel A has no gaps or atypical peaks or troughs with an approximately constant wheel rotation speed.

Two wheels

Channel A is as above.

Channel B displays a periodic (about every half a second) abnormality, causing an increased amplitude over a couple cycles. This is typical of a rotating component issue (the sensor is fixed), for example, a damaged reluctor ring.

Four wheels

In addition to Channel A and Channel B described above, Channel C and Channel D have been connected to the remaining wheel speed sensors, with both displaying good waveforms (Channel B remains faulty).

Waveform Library

Go to the drop-down menu bar in the lower left corner of the Waveform Library window and select, ABS or wheel-speed sensor (analog/inductive).

This example shows the waveform with either a faulty sensor, circuit or connection.

Example inductive ABS wheel speed sensor.

Further guidance

Wheel speed sensors provide wheel and road speed feedback to ABS and its derivative active vehicle safety systems (i.e. stability and traction control systems etc.).

These systems are designed to provide corrective action (e.g. wheel braking or engine torque limitation) when the vehicle or wheel speed(s) have exceeded their normal operational tolerances, for example, during conditions of wheel slip, oversteer or understeer etc. Wheel speed sensors are critical to the operation of these systems and, therefore, the safe handling of a vehicle.

Inductive wheel speed sensors encase a wire coil around a magnetically polarised core and operate in tandem with a pulse wheel mounted on a component rotating at wheel speed, for example, a driveshaft or hub. As the pulse wheel passes the sensor, the sensor's magnetic field is disturbed, which induces an oscillating voltage within the wire coil and the circuit connected to it. The quicker the wheel rotates, the greater the oscillation frequency and amplitude.

An ABS control module expects similar (within a given tolerance) oscillation frequencies from all the vehicle’s wheel speed sensors and uses any differences to calculate the timing and scale of its interventions.

If one or more wheel speed signals continuously fall outside of normal parameters the control module may turn the ABS function off. A driver warning light will be illuminated but, as with any electrical fault on ABS, normal hydraulic braking is maintained.

Wheel speed sensors and their pulse rings are exposed to the elements and have to operate under conditions of constant vibration and movement. As such, common faults are:

  • sensor signal failures, caused by chafed or fractured circuit wiring, sensor or connector corrosion, or incorrect sensor fitment; and
  • pulse wheel related problems arising from corroded or damaged teeth, incorrect pulse ring fitment (misalignment), contamination from a build-up of ferrous material, or an excessive air gap between the sensor and the pulse wheel.

Diagnostic trouble codes

Selection of component-related Diagnostic Trouble Codes (DTCs):

C0000 - Vehicle Speed Information Circuit Malfunction

C0035 - Left Front Wheel Speed Circuit Malfunction

C0036 - Left Front Wheel Speed Sensor Circuit Range/Performance

C0040 - Right Front Wheel Speed Circuit Malfunction

C0041 - Right Front Wheel Speed Sensor Circuit Range/Performance

C0045 - Left Rear Wheel Speed Circuit Malfunction

C0046 - Left Rear Wheel Speed Sensor Circuit Range/Performance

C0050 - Right Rear Wheel Speed Circuit Malfunction

C0051 - Right Rear Wheel Speed Sensor Circuit Range/Performance

C0221 - Right Front Wheel Speed Sensor Circuit Open

C0222 - Right Front Wheel Speed Signal Missing

C0223 - Right Front Wheel Speed Signal Erratic

C0225 - Left Front Wheel Speed Sensor Circuit Open

C0226 - Left Front Wheel Speed Signal Missing

C0227 - Left Front Wheel Speed Signal Erratic

C0229 - Drop Out of Front Wheel Speed Signals

C0235 - Rear Wheel Speed Signal Circuit Open

C0236 - Rear Wheel Speed Signal Circuit Missing

C0237 - Rear Wheel Speed Signal Erratic

C0238 - Wheel Speed Mismatch

C0245 - Wheel Speed Sensor Frequency Error

C0300 - Rear Speed Sensor Malfunction

C0305 - Front Speed Sensor Malfunction

GT003

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Premium 6-way breakout lead set

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • Large Dolphin/Gator Clips

    £10.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £47.00

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

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Guided test: ABS wheel speed sensor (inductive) - voltage